In valve controllers of said type, the variability of the control times and of the maximum lift of the gas exchange valve is attained in that, when the first hydraulic valve is open, a partial volume of the pressure chamber which acts as a so-called hydraulic linkage can be discharged in a continuously variable fashion into the pressure relief chamber, and accordingly the cam lift predefined by the camshaft is transmitted entirely, partially or not at all to the gas exchange valve.
A significant amount of responsibility for the functional reliability of the valve controller is consequently assumed by the first hydraulic valve, the switching function of which must be precisely and reproducibly ensured under all operating conditions of the internal combustion engine. There is however the risk, which can never be entirely eliminated, that the first hydraulic valve, which is open in the deenergized state, suffers a malfunction whereby it no longer closes. The result is an uncontrolled shutdown of the one or more associated gas exchange valves.
With regard to adequate emergency running capabilities of the internal combustion engine (limp-home mode), it is proposed in the generic DE 10 2008 049 181 A1 that the hydraulic system of the valve controller be expanded by a second hydraulic valve which is open during normal operation of the valve controller and closed in the event of a malfunction in order to break the connection from the pressure chamber to the pressure relief chamber. By means of said measure, even if the hydraulic valve is permanently open—for example on account of an electrical power failure or a mechanical defect in the first hydraulic valve—a pressure build-up in the pressure chamber adequate for transmission of lift to the gas exchange valve is made possible by virtue of the second hydraulic valve being closed during emergency running operation and preventing a release of pressure from the pressure chamber.